The present invention relates to an adjustable air intake, or draft control plate which is located in the air inlet portion of a forced air draft furnace for the purpose of controlling the air intake volume, thus insuring optimum combustion of the fuel in the furnace.
Forced air furnaces burning gas, coal, and oil are very prevelant in our society, especially in industrial and commercial applications. One common use of forced air furnaces is a "heater treater." As crude oil is pumped from oil wells, it contains many entrained impurities such as water, dirt and other solids, which will not settle out of the viscous crude oil. As this crude oil is pumped from the ground, it is pumped into a "heater treater" which raises the temperature of the crude oil. Since the heated crude oil has a lower viscosity, the entrained water, dirt and other solids can separate out and settle.
These heater treaters operate in remote pump locations, thus it is very desireable to have the forced air furnace operate with minimum operator control and maintenance. The present practice on the heater treaters is to place a manual control on the forced air intake in order to control the volume of the air intake. It is not uncommon for an improper manual adjustment of the air intake volume to throw the heater treater furnace into a mode where it oscillates between excess oxygen and an insufficient oxygen condition. Both conditions are extremely inefficient from the standpoint of fuel consumption and the latter can cause the heater treater to emit black smoke, thus falling below minimum air pollution standards. If this oscillation exceeds a predetermined value for minimum oxygen in the furnace, a safety mechanism immediately shuts down the heater treater furnace. The furnace shut down results in dirty crude oil being pumped into a storage tank, which in turn contaminates the rest of the oil in the storage tank. The particulate contamination levels in the storage tank may render the entire bulk of crude oil unsaleable without additional processing. Since the heater treaters are located in remote locations, it may be a matter of hours before someone comes along and restarts the furnace. Thus, there is a clear need for a more reliable system which regulates the air intake on forced air furnaces.
Additionally, the heater treater furnaces are constantly being turned on and off as the temperature and volume of the incoming crude oil varies. When the forced air furnaces are initially turned on, or shut off, the amount of air required to operate the furnace at its optimum conditions goes through several oscillations before settling out to a relatively constant volume of air. A fixed opening on the air intake does not provide for efficient furnace operation during these start up and shut down transients. Thus, there is a need for a fast operating, automatic controller on the air intake in order to make the furnace operation more efficient during the start up and shut down transients.
Another example of forced air furnaces used in the oil industry is a steam generator. In order to increase the oil production of wells, it is common practice to inject hot water or steam into the ground in order to make the crude oil less viscous and, hence, easier to extract. In order to provide a measure of control, the temperature of the oil casing is monitored and used to determine the temperature of the steam being injected into the ground. Present forced-air systems control both the air intake rate and the rate of fuel consumption in an attempt to vary the temperature of the injected steam. These numerous variables lead to a complex instrumentation system for controlling the forced air furnaces. The complexity is increased on some steam generating systems which controllably recycle the vent gas in order to increase the temperature of the incoming air and to decrease the oxygen going to the furnace.
The large number of variables which can affect the optimum operation of these forced air furnaces, leads to a significant amount of operator discretion in determining furnace operation. Since each operator exercises his or her discretion differently, the efficiency of the operation of the forced air furnaces varies considerably. It is thus desireable to have a simple, yet efficient operational method for the forced air furnace which will minimize the discretion of the operator.